1. Field of the Invention
The present invention relates to battery feed and line feed resistors as used in telephone line circuits and more particularly to a thick film resistor capable of withstanding high voltage pulses yet capable of fusing at low continuous current.
2. Description of the Prior Art
Line feed and battery feed resistors are susceptible to lightening strikes and therefore must be capable of withstanding such high voltage pulses. However, in order to protect telephone central office circuits, the line feed and battery feed paths must be broken when continuous extraneous current at even low levels, is applied to these resistors. The conventional solution to this problem is to use a discrete resistor, capable of withstanding lightening surges, in series with a fuse. However, this solution is expensive in terms of both cost and space.
The present invention solves this problem by using a low cost thick film resistor in place of both a high voltage resistor and a fuse.
Accordingly it is the object of this invention to provide an economical solution to the problem of protecting telephone central office circuits with line feed and battery feed resistors that can both withstand high pulsed power, and fuse at low continuous power levels.